Method and apparatus for MRI

Abstract

In order to narrow the dynamic range of an NMR signal and to provide MRI of low cost and high image quality without inducing the distortions of an image other than distortion of phase which can be corrected or the degradations of the measurement accuracies of various parameters, a coil for generating an inhomogeneous magnetic field which varies slowly within region to-be-imaged is added to a coil for generating a static magnetic field of high homogeneity, and current to flow through the former coil is changed so as to control the inhomogeneous magnetic field.

We claim: 
     
       1. A magnetic resonance imaging apparatus comprising means to generate a static magnetic field, a gradient magnetic field and a high-frequency magnetic field; inhomogeneous field generation means to additionally generate a spatially inhomogeneous magnetic field in a region to-be-imaged; means to detect a nuclear magnetic resonance signal from an object to-be-examined; means to convert the detected signal into digital data; and means to subject the digital data to various calculations including reconstruction of an image; wherein said inhomogeneous field generation means includes means to generate a pulsed inhomogeneous magnetic field. 
     
     
       2. A magnetic resonance imaging apparatus comprising means to generate a static magnetic field, a gradient magnetic field and a high-frequency magnetic field; inhomogeneous field generation means to additionally generate a spatially inhomogeneous magnetic field in a region to-be-imaged so as to narrow a dynamic range of a nuclear magnetic resonance signal; means to detect a nuclear magnetic resonance signal from an object to-be-examined; means to convert the detected signal into digital data; and means to subject the digital data to various calculations including reconstruction of an image; wherein said means to subject the digital data to various calculations further includes means to eliminate influences of the inhomogeneous magnetic field on the reconstructed image. 
     
     
       3. A magnetic resonance imaging method comprising the step of generating a static magnetic field, a gradient magnetic field and a high-frequency magnetic field; the step of additionally generating a spatially inhomogeneous magnetic field in a region to-be-imaged; the step of detecting a nuclear magnetic resonance signal from an object to-be-examined; the step of converting the detected signal into digital data; and the step of subjecting the digital data to various calculations including reconstruction of an image; wherein the step of additionally generating the inhomogeneous magnetic field includes generating a pulsed inhomogeneous magnetic field. 
     
     
       4. A magnetic resonance imaging method comprising the step of generating a static magnetic field, a gradient magnetic field and a high-frequency magnetic field; the step of additionally generating a spatially inhomogeneous magnetic field in a region to-be-imaged so as to narrow a dynamic range of a nuclear magnetic resonance signal; the step of detecting a nuclear magnetic resonance signal from an object to-be-examined the step of converting the detected signal into digital data; and the step of subjecting the digital data to various calculations including reconstruction of an image, wherein the step of subjecting the digital data to various calculations further includes eliminating the influences of the inhomogeneous magnetic field on the reconstructed image.